1. Field of the Invention
The present invention broadly concerns apparatus for initiating drop-out motion of a latched electronic sectionalizer tube for isolating a branch or lateral line of a high voltage power distribution system. More specifically, the invention is directed toward a resettable sectionalizer actuator assembly having an electronic solenoid which, upon energization, releases a spring-loaded plunger. In turn, the unlatched plunger exerts, either directly or indirectly, a force on a trunnion member sufficient to release the member from its normally latched, stationary disposition and initiate pivotal movement of the member for drop-out of the sectionalizer tube toward an isolated position.
2. Description of the Prior Art
devices known as automatic reclosers or reclosing circuit breakers are often used to protect the main supply line as well as lateral lines of a high voltage power distribution system. The recloser is operable to sense the magnitude of current flowing through the main supply line and disable the entire downstream distribution system if currents above a certain magnitude are detected. After a short period of current interruption, the recloser automatically re-energizes the circuit unless excess current conditions are again subsequently sensed.
In many instances, electronic sectionalizers are installed at the beginning of each lateral line of distribution systems having an automatic recloser or reclosing circuit breaker. Each sectionalizer cooperates with the recloser bu disabling the respective lateral line served by the sectionalizer during a subsequent dead portion of one of the opening and closing sysles of the recloser if current conditions in the lateral line are greater than a certain, pre-selected value. In this manner, current flow may be automatically restored to the remaining lateral lines duyring a subsequent closing cycle of the recloser.
Preferably, electronic sectionalizers for outdoor use are physically interchangeable with conventional electrical cut-outs so that the sectionalizer can be easily installed in retrofit fashion in the mounting structure originally provided to hold the cut-out. Normally, then, electronic sectionalizers include an alongated tube assembly having an upper conductive portion releasably engageable with an upper contact of the cut-out mounting structure, and a pivot mechanism received on a lower contact of the mounting structure. The elongated tube conducts current between the upper contact and the pivot mechanism in engagement with the lower contact of the mounting structure, and a sensing device mounted on the tube detects the magnitude of current. The tube also carries a logic circuit coupled to the sensor which typically fires a one-shot chamical actuator once the logic circuit has determined that over-current conditions exist in the lateral line protected by the sectionalizer after one or more cycles of operation of the reclosing apparatus.
In the past, chemical actuators of electronic sectionalizer assemblies were arranged to release or open a latch to initiate drop-out motion of the sectionalizer tube away from its normal upright orientation conducting current between the upper and lower mounting structures and toward an open-circuit orientation wherein the top of the tube is spaced from the upper mounting structure. As an example, U.S. Pat. No. 4,553,188, dated Nov. 12, 1985 illustrates a sectionalizer having a chemical actuator that, once fired, causes a latch or release lever to swing toward an out-of-the-way position and thereafter enable a spring and/or the forces of gravity to initiate pivotal movement of the sectionalizer tube and enable the tube to swing away from the upper contact. Another example of a chemical actuator and pivot mechanism for a sectionalizer is described in U.S. Pat. No. 4,636,764, dated Jan. 13, 1987 wherein the actuator is positioned to release a toggle mounting lever from an over-center position for subsequent drop-out of the sectionalizer tube away from the upper mounting structure.
In a co-pending application entitled "Latch and Pivot Mechanism for Electronic Sectionalizer Mounting Structure", filed Sept. 11, 1987, Ser. No. 07/095,548 and assigned to the assignee of the present invention, an electronic sectionalizer is provided with a chemical actuator that is positioned to strike, upon firing, a trunnion member for immediate drop-out of the sectionalizer tube with minimal reliance upon a spring or the effects of gravity. A latch is provided for normally holding the sectionalizer tube in a loaded, non-over-center position, and substantially the entire force of the chemical actuator is imparted directly upon the trunnion member to ensure reliable and rapid motion of the sectionalizer tube toward a disabled, open circuit orientation.
However, there is a long felt need for a resettable actuator assembly for an electronic sectionalizer so that the cost of replacing chemical actuators can be eliminated. Each chemical actuator must be replaced once fired, and thus utilities are faced not only with the cost of purchasing and maintaining a sufficient number of actuators on hand at all times but also with the expense of labor for installing the actuators and connecting leads to the actuator to the logic circuit.
In U.S. Pat. No. 3,321,721, dated May 23, 1967, a mechanical sectionalizer is described that includes an electric solenoid and plunger assembly which is arranged to release a latch for subsequent drop-out movement of the sectionalizer away from its mounting structure. The latch of U.S. Pat. No. 3,321,721 is in the form of a swingable lever which, when pivoted by the solenoid plunger, releases a second lever normally holding the sectionalizer in a current-carrying orientation; subsequently, the second lever swings about a pivot under the influence of gravity until the top portion of the sectionalizer assembly has fallen away from upper mounting structure and toward a current disabled or drop-out position. However, the dual swinging lever arrangement shown in U.S. Pat. No. 3,321,721 is somewhat unsatisfactory in that a certain amount of time is needed subsequent to release of the second lever for enabling the latter to gain momentum and swing in an arc a sufficient distance to allow the upper portion of the sectionalizer tube to drop away from the upper mounting structure.
Moreover, outdoor sectionalizers installed on cut-out mountings are exposed to rain, ice, and extreme swings of temperature. The pivot mechanism is normally held in a stationary position for extended periods of time and is therefore subject to the effects of corrosion, ice, or debris which may eventually prevent successful drop-out of the sectionalizer tube. Consequently, it would be advantageous to provide a latch and pivot mechanism for an electronic sectionalizer which would reliably disable the branch line as needed, and yet could be re-set for subsequent use without the trouble and expense of installing a one-shot chemical actuator.